The present invention relates to structural panels and more particularly concerns such panels and methods for their manufacture that employ filler materials, having certain desirable properties, together with reinforcing structures to provide a unitary panel structure.
Lightweight plastic materials, including the many different types of foamed synthetic resins and expanded plastic foams, such as urethanes, polystyrenes, and the like, have a number of properties that are highly desired in building materials for various types of structures such as walls, roofs and the like. These properties include light weight, exceedingly low thermal conductivity, resistance to abrasion, impermeability to moisture, and acoustic insulation. However, such materials generally are deficient in structural strength and therefore must be combined in some manner with other materials having satisfactory structural properties.
Various configurations employing combinations of lightweight cellular plastic foams or expanded plastic bodies and rigid load-bearing structural elements have been suggested in the past for providing structural building panels that can effectively utilize the desirable properties of the cellular materials. Typical of such prior art arrangements, are the U.S. Pat. Nos. to Weisman 3,305,991, 3,555,131 and 3,879,908. In U.S. Pat. Nos. 3,305,991 and 3,555,131, there is described a structural panel and a technique for manufacture thereof in which a three-dimensional reinforcing framework is first built up and then a lightweight plastic core is formed in situ within the framework, and positioned so that the outer surfaces of the resulting foamed in place core are hopefully located inwardly of the outer boundaries of the three-dimensional framework. It is desired to have the framework extend outwardly of the core so that the hybrid panel, the combination of cellular material and rigid framework, may be coated with plaster, gunnite, stucco or the like, in which the projecting portions of the structural framework may be embedded. However, because the cellular material is foamed in place, a form must be provided to define the bottom surface of the foam core. Since this form must be positioned above one outer side of the prefabricated structural framework, difficulties are encountered in maintaining the form in a planar configuration and in positioning the form at a precise distance from the outer surface of the framework.
Further, since no form is generally employed to define the upper surface of the foamed in place core (the panel core is foamed in place within the structural framework, with the panel in a horizontal position according to the teaching of the patents), the foam core will exhibit an outer surface that is far from the desired planar condition. It will exhibit a surface of such irregularity and imprecise location that the foam core may actually contact the outer elements of the structural framework in many places, thereby preventing a subsequent coating from completely encompassing such outer portions of the framework.
The later U.S. patent to Weisman No. 3,879,908 avoids some problems of the use of foamed in place material and instead, after building a completed three-dimensional structural framework that covers the entire panel on all six sides thereof, inserts a plurality of insulative elements through passages that are disposed wholly within the structural framework. These insulative elements must be dimensioned so as to freely and easily pass between adjacent elements of the structural framework and, when positioned, will not have adjacent surfaces in contact with one another. Impermeability to moisture is thereby greatly degraded. Thereafter a bonding agent is employed in the arrangement of the Weisman U.S. Pat. No. 3,879,908 to secure the insulative elements in position within the lattice. This bonding agent is a layer of material that is foamed in place; but in a somewhat thinner layer than the remainder of the core, and is employed to bond the insulative elements to the metal elements of the structural framework. This is a time-consuming and expensive procedure, and still provides a panel surface formed by a foamed in place bonding agent. Such surface may be irregular and improperly positioned with respect to the outer surface of the structural framework. Further, since the insulative elements must be inherently spaced from one another in order to allow them to be inserted into the passages in the structural framework, they can form no vapor or moisture barrier. Their heat and sound insulating properties also are significantly degraded by virtue of the space between adjacent insulating elements, even though the ends of such spaces are covered by the foamed in place bonding agent.
Accordingly, it is an object of the present invention to provide a composite structural panel that avoids or minimizes above-mentioned problems.